This invention pertains to magnetic media storage devices where data and servo information are stored in adjoining tracks and more particularly to a structure and method for more effectively writing servo data on the media of such a device.
Servo tracks for magnetic media recording are normally offset a half-track pitch from the associated data tracks whereupon the servo reading is accomplished by sensing the signals from two adjoining servo tracks and establishing the proper data track location by adjusting the servo head position until the signals read from the two interfacing tracks are of equal magnitude indicative of positioning on the centerline of the associated data track or tracks. Data tracks are spaced from adjoining data tracks and only occupy about 80 percent of the track pitch; however, servo tracks are recorded with a width equal to the full track pitch or spacing between adjoining track centerlines. Consequently any condition that impairs the servo track width makes the system less accurate and less effective.
The phenomena that is the principal factor in impairing the adjoining track of a properly operating servo writing system is the fringe field which exists transversely beyond the recording head that confronts the media and is intended to define the width to which the magnetic signals are written. Thus, the head will write significantly wider than the physical core width. This writing beyond the core width erases previous data and replaces it with very low resolution signals. Subsequently, when a servo read head is attempting to seek the data track centerline, the servo track interface which should present signals of equal strength at either side presents a full strength signal at the edge of the servo track most recently written and a degraded signal along the confronting edge of the adjoining track previously written. As track densities increase, and track widths correspondingly decrease, the effect of this degraded region becomes a greater and greater percentage of the signal.